Numerous machines for this purpose have already been proposed. Examples of the latter may be found in documents U.S. Pat. No. 4,694,975, U.S. Pat. No. 4,876,842, U.S. Pat. No. 5,046,300, and U.S. Pat. No. 5,127,208.
Most of the known automatic machines for the molding, filling, and closing of wrappings based on films of a thermoplastic material comprise:
a molding collar which receives the intake film in a flat state from an unwinding device, and provides film formed into a tube at the output; PA1 a filling spout which opens into the molding collar and consequently into the tube; PA1 means for longitudinal welding so as to weld the edges of the film and close the tube longitudinally; and PA1 suitable means for sequentially generating an initial transverse weld before a product is introduced into the tube by means of the filling spout, then a second transverse weld when the product has been introduced into the tube so as to close the wrapping around the product.
The film may be pre-equipped with closing profiles prior to its arrival on the collar or, as a variant, the machine may comprise means for feeding the film with a closing profile, preferably profiles with complementary male and female grooves, and suitable means for attaching the profiles to the film by welding.
These machines have already been very useful.
Nonetheless, they are not completely satisfactory.
In particular, especially in thermoplastic material, the presence of pleating in the sheets making up the sides of the wrapping obtained is sometimes noted.
On the one hand, such pleating hinders the transverse welding operations by reason of the excessive thicknesses which it produces, and because of this may create shortcomings in imperviousness.
On the other hand, such pleating degrades the esthetics of the wrappings obtained.
Different arrangements have already been proposed to attempt to eliminate such pleating.
In particular, means comprising tongs have been proposed, most often controlled by jacks or the equivalent, to stretch out the film in its widthwise direction. On this point, reference might be made, for example, to documents FR 2638419, EP 0319995, and U.S. Pat. No. 4,829,745.
The Applicant itself proposed, in document FR 2716160, an improvement consisting in an unpleating system comprising at least two suction-cups positioned on both sides respectively of the wrapping bags and capable of relative travel in a general direction parallel to the transverse welding lines.